Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$150.60	10.762%	$166.8076	$166.81	$166.80	$166.80
Purchase #2	$37.43	4.281%	$39.0324	$39.03	$39.05	$39.00
Purchase #3	$88.69	12.734%	$99.9838	$99.98	$100.00	$100.00
Purchase #4	$39.58	9.116%	$43.1881	$43.19	$43.20	$43.20
Purchase #5	$47.44	7.151%	$50.8324	$50.83	$50.85	$50.80
Purchase #6	$208.84	8.414%	$226.4118	$226.41	$226.40	$226.40
Purchase #7	$41.88	8.841%	$45.5826	$45.58	$45.60	$45.60
7 purchase totals =	$614.46		$671.8387	$671.83	$671.90	$671.80